1. Field of the Invention
The present invention relates to an automotive supercharging apparatus, and particularly relates to an automotive supercharging apparatus to which a centrifugal compressor is mounted that can be driven by both an engine shaft and an electric motor-generator shaft.
2. Description of the Related Art
Automotive supercharging apparatuses that function as superchargers that receive torque from a belt and a pulley that are connected to an engine pressurize air that is used by the engine to enable the engine to burn a larger quantity of fuel, thereby increasing output and torque. There are two basic types of these automotive supercharging apparatuses: positive displacement; and centrifugal. Centrifugal automotive supercharging apparatuses are more efficient than positive displacement ones, and are more lightweight, but one problem is that supercharging capacity is insufficient in low-speed regions.
Thus, multistage speed apparatuses have been proposed in which epicyclic gear sets that have a high gear ratio arrangement and a low gear ratio arrangement are disposed, and deficiencies in supercharging capacity in the low-speed region are relieved by switching to the epicyclic gear set that has the high gear ratio arrangement up to a predetermined engine speed, and switching to the epicyclic gear set that has the low gear ratio arrangement in excess of the predetermined engine speed (see Patent Literature 1, for example).
However, there is a limit to how much the gear ratio can be increased in the configuration of the epicyclic gear sets according to Patent Literature 1, and supercharging capacity of the centrifugal supercharging apparatus is insufficient in a micro-low velocity rotational frequency range from idling to approximately 1,500 rpm. Activation during engine shutdown is also fundamentally impossible, preventing sufficient boost pressure from being achieved immediately after restarts from idling reduction, etc. In diesel engine vehicles in particular, when turbo lag arises, the amount of air is insufficient, increasing particulate matter (PM).
In view of these conditions, superchargers have been proposed that include: a motor; a compressor that is disposed in an air intake system of an engine; a planetary gear mechanism that has: a sun gear that is connected to a drive shaft of the engine; planetary gears that are connected to the motor; and a ring gear that is connected to the compressor; and a control unit that drives the motor to control rotational speed of gears of the planetary gears, and control a rotational speed of the compressor independently from the rotational speed of the engine by controlling the rotational speed of the gears of the planetary gear (see Patent Literature 2, for example).
Electronically-controlled supercharging apparatuses have also been proposed in which a supercharger is driven only by a switched reactance electric motor to which power is supplied by a battery and is controlled independently from the rotational speed of the engine (see Patent Literature 3, for example).
Patent Literature 1: Japanese Patent Laid-Open No. 2002-242687 (Gazette)
Patent Literature 2: Japanese Patent Laid-Open No. 2004-360487 (Gazette)
Patent Literature 3: Japanese Patent No. 3686645 (Gazette)
In the technique according to Patent Literature 2, since it is necessary to introduce an additional motor that controls the rotational speed of the compressor, and the planetary gears, the sun gear, and the ring gear are coupled to three shafts, i.e., to the motor, to the engine, and to the compressor, one disadvantage has been that the construction of the planetary gear mechanism is complex and a high degree of control is required, increasing cost. There have also been other problems such as rotational speed control of the compressor no longer being possible if the motor fails, making continuation of operation practically impossible.
In the technique according to Patent Literature 3, because the supercharger is driven by an electric motor, one problem has been that continuation of operation becomes practically impossible if the electric motor fails. Because the supercharger is driven in a high-speed rotation region, there have also been other problems such as the electric power that is demanded of the electric motor exceeding 1 kW, requiring a high-capacity inverter and battery in low-voltage systems in the vehicle, such as the 12 V system, etc., making significant cost increases unavoidable.